# Fermi surface, possible unconventional fermions, and unusually robust resistive critical fields in the chiral-structured superconductor AuBe

## TL;DR

This study investigates the electronic structure and unconventional superconductivity in AuBe, revealing complex Fermi surface features, possible topologically protected surface states, and robust critical fields in a chiral noncentrosymmetric superconductor.

## Contribution

It provides the first validation of AuBe's bandstructure via dHvA oscillations and links unconventional fermions to its superconducting properties.

## Key findings

- Validation of bandstructure through dHvA oscillations
- Observation of nonstandard field dependence linked to unconventional fermions
- Resistive critical fields exceed thermodynamic measurements, suggesting topological effects

## Abstract

The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65~T and temperatures down to 0.3~K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas-van Alphen (dHvA) oscillations has allowed the calculated bandstructure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved.